Machine and method for grinding hobs and the like



Marh 5, .1946 A. cHMlD-r 2,395,9l@

MACHINE AND METHOD FOR GRINDING HOBS AND THE LIKE L E S INVENTOR.

\ Hl 7 3 LIONELA.scm/NDTi ATTORNFYS March 5, IOG.

A. SCHMIDT 2,395,910 MACHINE AND METHOD FOR GRINDING HOBS AND THE LIK Filed May l5. 1942 6 Sheets-Sheec 2 INVENTOR. LIONEL'ASCHMIDT Bm, MM q ATTORNEYS March 5, 1946. l.. A. scHMlD'r MACHINE AND METHOD FOR GRINDING HOBS AND THE LIKE Filed May 15.l 1942 le sheets-sheet s 4 INVENTOR.

UONEL A. SCHMIDT ATTORNEYS March 5, 1946. 1,. A. scHMmT 2,395,910'

MACHINE AND METHOD FOR GRINDING HOBS AND THE LIKE y Filed May 15. 1942 6 Sheets-Sheet 4 m INVENTQR l LKONELASCHMIDT BY ATTORNEYS L. A. SCHMIDT March 5,- 1946K MACHINE AND METHOD FOR GRINDING Hos AND TEE LIKE Filed May l5, 1942 6 Sheets-Sheet 5 INVENTOR,

LIONEL AECI-MDT ATTORNEYS March 5, 1946.q l.. A. SCHMIDT i 2,395,910 y xA f TTF-H Patented Mar. 5, 1946 2,395,910 AND METHOD Foa GRINDING MACHINE HOBS AND THE LIKE Lionel A. Schmidt, Fairview Village, Ohio, assignor to The National Tool Company, Ohio, a corporation of Ohio Cleveland, I I

Application May 15, 1942, Serial No. 443,138

19 Claims.

The present invention relates to a machine and a method for grinding rotary, toothed cutting grinding if different rangesof-pitches of hob teeth were to be produced.

tools such as hobs and thread milling cutters.

Grinding oi the teeth of hobs and like cutting tools constitutes afinish machining Voperation necessary to impart the final precision and accuracy, within closely specified limits of tolerance, to the teeth of the cutting tool. Any opportunities for errors or departures from accurate operation, either in the grinding machine itself, or dependent upon human factors involved in the manipulation of the machine or the performance of the grinding process, are all necessarilyk reflected in the degree of accuracy obtainable in the ground hob product and the time and cost involved therein. It is the general object and nature of my present invention to provide a machine for grinding hobs and the like in which such opportunities for machineimparted errors are reduced many fold; and a novel method of grinding dependent required human manipulationsand in which variations from one step to .the other were most likely to occur.

for its steps of operation upon suoli machine. My new grinding process .eliminates previously i Since the helical screw threadv of'a' feed screw is generated by point moving in three dimensions, viz., both axially and circumferentially, there is necessarily an inherent dimculty in controlling th'e precision and accuracy of its manufacture. As derived from the mathematical formula for the. helix, viz:

Length of seinem/(afnam it will be seen, that there are threev variables determinate thereof, namely, the number of turns (n), radius of the base cylinder (r) and the axial pitch (h). v n

The grinding machine embodying' the principle of my invention utilizes the motion generated by a point moving in single plane and progressively away from a fixed centeras the controlling means for effectingthe axial traverse of the hob spindle with respect to the grinding wheel. `An involutecam surface comprises a ,preferred embodiment of such a 4,motion-genery whichrhave here-A tofore been found necessary in grinding zhobs,

The movement which a bob undergoes with rei vspect to a grinding wheel in the hob tooth grinding operation is both rotative and axial. Heretofore, the axial movement in hob grinding l3machines has been obtained by the well known ma- A chine tool element consisting of the feed screw. Such a feed screw movement has been transmitted either directly to the hob spindle. as in U. S. Patent No. 1,667,488, 0r to a slidable hob spindle carriage, as in U. S. Reissue Patent No.

18,247. or to the grinding wheel carriage, as disclosed in American Machinist, issueof Aug. 23,

1906, pages 231-236, or to a sine bar Which is in turn connected to the hob spindle carriage as in U. S. Patent No. 1,989,792. In all of these prior expedients, the accuracy and uniformity of the axial movement of the hob with respect to the i grinding wheel was, of course, dependent upon the accuracy of the manufacture of the feed screw in the rst instance. Any variation or discrepancy in the helical contour of the thread 'l surface on the feed screw from that of a true helix, whither due to errors in original manuating means, andby employing such acam feed movement, I eliminate 'the opportunities of error that occur not only throughout the relativelyl long. attenuated surface of va helical screw thread, but also provide a movement controlling element which is more readily susceptible of accurate an precise manufacture in the first instance because an involute is generated by a point moving only in two dimensions, viz., the end ofv a tangent `vunwound from a fixed base circle in a single facture or subsequent wear from use, wouldH necessarily be reflected in the finished ground hob product. Furthermore, it was necessary to provide a set of feed screws of different pitch for plane, as compared to the three dimensional generating movement of a helix. This latter fact is further emphasized by the mathematical formula for an involute,v where:

Length of involute=1/2 c (rad 11.)2

Thus, in the involute, there are only two determining variables, namely, the radius of the base circle (c) andthe angle (u), measured in radians, of the radius of the ibase circle to the Y point of .tangencyof the generating tangent.

The length of the surface of an involute cam necessary to impart a'given axialmove'ment to the hob spindle is/only a fraction of that required by the length of surface of a feedscrew. Thus, by reason of my invention, I not only reduce to a considerable extent the possibilities of errors in the manufacture of the 'movement-controlling surface in the first instance. but also reduce to about 11s or greater the extent of such controlling surface for the same and given amount of machine movement.

The above-outlined novel means for imparting axial traverse to the hob with respect to the grinding wheel gives rise to an interdependent and co-related` novel process for grinding hobs and similar toothed cutters. Since the direction of rotation ofthe hob is not dependent upon the axial movement-controlling action of the earn, it is possible to reverse the direction of rotation of the hob spindle to grind both sides of the hob teeth with respect to one and the same axial movement controlling surface. Again, such procedure was not practicable or feasible in the previously employed feed screw axial movement grinding machines because, upon reversal of rotation of the hob spindle, there would be required a corresponding reversal of direction of rotation of the feed screw. with the net result that the axial movement of the hob spindle would be controlled by the opositeside of the thread screw. This meant that an entirely diiierent dividual differencesY and errors of contour, would have to be ,used upon reversal of the rotation of the hob spindle.

Further. by rendering possible and practicable the reversal of rotation of the hob spindle. my new hob grinding process possesses the additional advantage of permitting both sides of the teeth of the hob to be ground from front to ba ck without moving` the grinding wheel to a new position, ap` proximatelyv 180 removed. when the change is made' from grinding one side of the hob teeth to grinding the other side thereof. This advantage eliminatesv certain "setting up" errors. as well as the time and labor involved therein. in moving the grinding wheel to a completelydifferent position with respect to the-hob axis. over and above the required disconnecting. changing and re-connecting of the power drive to the grindingr wheel.

The foregoing statements have outlined the essential novel features and improved results achieved by the principle of my invention. Additional objects-and advantages. explained in more detail. Vshall become apparent during the following description.

To the accomplishment of the foregoing and related ends. said invention. then. consists of the means hereinafter fully described and particularly pointed out in the claims. the annexed drawings and the following description setting forth in detail certain means and one mode of carryingr out ,the invention. such disclosed means and mode illustrating. however. but one of various ways in which the principle of the invention may be used.

In said annexed drawings:

Fig. 1 is a. vertical sectional view taken through a hob grinding machine embodying the principle of my invention:

Fig. 2 is an enlarged. detailed.` sectional View of the involute cam drive mechanism and taken substantially along line 2 2 of Fig. 5 and in the directi on ofthe arrows:

Fig. 3 is an enlarged. detailed sectional view of the involute cam drive mechanism taken upon a plane normal to that of Fig. 2 and substantially along the lines 3 3 of Figs. 2 and 5 and in the direction of the respective arrows:

Fig.' 4 is a detailed end elevational view of the worm bearing adjustment mechanism of Fig. 2;

Fig. 5 is ran enlarged, horizontal, sectional view of the left-hand top portion of Fig. l;

Fig. 6 is an end elevational view taken from the left-hand end of Fig. 1; A

Fig. 7 is a top plan view, partially in section, of

the mechanism shown in Fig. 1;

Fig. 8 is an enlarged, detailed view taken along the line 8 8 and in the direction of the arrows as shown in Fig, 7;

Fig. 9 is a more or less diagrammatic View i1- lustrating the relative position and movement of the hob with respect to the grinding wheel during the grinding of one side of the hob teeth;

Fig. 10 is a more or less diagrammatic view taken upon a plane normal to that of Fig. 9;

Fig. 11 is' a view similar to Fig. 9 but showing the parts in position for grinding the opposite side of the hob teeth; and

Fig. l2 is la view similar to Fig. l0, but taken upon a plane normal to that of Fig. 11 and illustrating the corresponding operation of the latter.

Now referring more particularly to Figs. l and 7 of the drawings, the machine shown therein comprises the base member I and the work supporting shaft or. hob spindle 2, which is rotatably and axially longitudinally mounted in the bearings 3 and 4 located in the upper housing member 5. The largel gear wheel or bull gear 'I is keyed and mounted upon the spindle 2, and meshes with the smaller or long pinion 8. The lo'g pinion 8 is of such a length as to remain in mesh with and accommodate the full extent of the longitudinal movement of the bull gear 1 as it traverses longitudinally with the spindle 2. The long pinion 8 is mounted upon a drive shaft 9 which in turn is driven by a sprocket I0 connected by means of the drive chain I I which, as shown in Fig. 6, is in turn connected to a reduction and reverse gear mechanism I I' and thence to the drive motor D.

As shown in Figs. 6 and 7, the drive shaft 9 is connected through the gears l2 and I3 to the counter-shaft I4 which leadsI to the left-hand end of the housing 5. and in turn connects through the change gears I4', l5, I6, I'I, I8 and I9 to the worm shaft 20. supported in the ball-bearings as indica-ted at 2I and carries the worm gear 22. The bail-bearings 2I are in turn housed eccentrically in the tubular or sleeve housing 23 which is mounted in the machine housing5. As best shown in Fig. 3, it will be seen that the sleeve housing 23 has its inner bore, in which the bearings 2| are mounted, slightly off center with respect to its outer wall, so that rotation of the sleeve 23 will result in a lowering or raising of the center of the shaft 20 with respect to the housing 5. The relative rotative position of the sleeve housing 23 in the housing 5 is accommodated by means of the flange 24 on the outer end of the sleeve 23 and secured thereto such as by the socket head or Allen head screw studs 25. The flange 24. seated in a complementary recess in the housing 5. is rotatably adjustable therein by means of the socket head screw studs 26 passing through the elongated arcuate slots 21 in the flange 24.

The worm gear 22 meshes with the worm wheel 3D on the transverse shaft 3|. By adjusting the relative rotative position of the sleeve housing 23, initial correct adiustment of the worm 20 with respect to the worm wheel 3U. or compensatory adjustment for wear. is obtained.

The shaft 3i is ,iournaled in the bearings 32 and 33 and carries the involute cam 34.

The cam surface of the cam 34 is generated by a point moving in an involute path about the center O of the basecircle C, and bears against the hardened surface of the plug 35 mounted in the left-hand hollow end of the spindle 2. Thus.

as the shaft3I rotates in a counter-clockwise velocity, the spindle 2 is caused to move in a right-hand direction'along' its axis'at a uniform rate of linear travel. Rotation of the involute vcarri 34 for only a portionof a revolution, viz.,

- on the end of the spindle 2 (i. e. a hob measuring 4 inches fromend to end) 4is yapproximately 8 inches of travel of the surface of the involute cam 34 across the end 35 of the spindle 2. A feed screw designed for accommodating the same amount of axial traverse of the hob spindle, for example, would be 21/2 inches in diameter, 1/3 inch axial screw thread pitch, and according to formula b, as heretofore given, would be approximately 94 inches in length of its helical thread surface, constituting the surface of reference determining and controlling the longitudinal traverse of the hob spindle. It will thus be'seen that any local variations in the manufacture and generation of the cam surface of 'my involute cam 34 controlling the longitudinal movement of the spindle 2 have less than 5, or more specifically, approximately Tg, the opportunity of occurrence than in a correspondingly required feed screw, when viewed from the standpoint of length of movement controlling surface alone.

A cup-shaped collar 36 enclosing the bearing 3 1 is mounted against a shoulder on the outside end of the hog spindle 2 and the lock' nut 38 engages against the inner race of the bearing 31. Eye bolts extend from lugs 36' (see Fig. '1) on the collar 3E and are engaged by the hooks 40 on the ends of the iiexible cables 4I which pass over the pulleys 42 and are both connected by means of an equalizer yoke 43 to the counterbalance weight 44.

The grinding wheel G (see Figs. 1 and 1) is mounted upon the shaft 50 which is journaled in the housing l. A drive pulleyy52 is carried on.

the outer end of the shaft 5U and connected to a drivemotor (not shown). A suitable dressing tool mechanism 53 is mounted adjacenty the grinding wheel G.

The grinding wheel shaft housing 5| is mounted upon a slide 54 which is in turn mounted upon r the main slide 55 and adjustable thereon by the usual feed screw and hand wheel mechanism such as indicated at 55. The main slide 56 is reciprocable in a direction transverse to the,hob spindle 2 by means of a cam and lever mechanism shaft 52. Thenut 1I holds the sleeve El, coupling 69 and hand wheel 10 on the shaft 62. Thus, by removing the .nut 1l and the studs 68, the cam 60 and sleeve 6l maybe removed from' the end of the shaft 62 and a diierent cam reinstalled, viz., either a cam of different contour Aor hand, such as for Ipurp'osescf reversing the cam actionas will be subsequently described.

As best shown in Fig. 8, a lever 15 is pivotally mounted upon the base frame Il of themachine as indicated yat16. The short or upper end of the lever 15 is inthe forrn of a cam surface 11 .terminating in a'notch or recess 18. rThis cam surface 11 is adapted to bear against a pin 19 projecting laterally from the grinding wheelslide 54. Thus, by raising the 1ever'15 tothe dotted line position shown in Fig. 8, the grindingfwheel slide 54 and its attached main slide 5'6 is moved in a backwardv direction against the tension of the spring 80 to a position Where the lever 51 is out of contact with the cam 50. When the pin 19 ts into the notch 18, the lever 15 is held in such position in the mannerof a detent and,

correspondingly, the slide 56 and the lever 51 are held in ysuch shifted position. y Operation of the lever 15 thus renders the reciprocating connection between the cam B0 and grinding wheel slide 56 inoperative, and is essentially for the purpose of facilitating temporary Vtesting or checking operationsV upon the hob, involving the removal ofthe grinding wheelG out of contact therewith, without disturbing the correct grinding position adjustment ofthe grinding wheel upon resumption of grinding operation.

The operation of the above-described machine and my new method for grinding hobs and the like is as follows, being'best illustratedby'reference to Figs. 9-12, inclusive: K

Fia@ represents a right-hand hob H in position with respect to the grinding wheel G forgrinding the side faces A of the hob teeth. The'hob f spindle 2 is vrotated in' such a direction as to cause the hob to rotate in a direction toward the front ends F of its teeth. and substantially as indicated bythe arrow in Fig. 10. The grinding wheel G is placedin such position as to make-a grinding cut upon the side A of the hob teeth, and as the hob spindle is traversed in an axial direction from left to right under the movement controlling action ofthe involute cam 34, the grinding wheel G passes across faces A of each one of the hobI teeth in a helical path from the right hand such as that illustrated inV Fig. 10. Thus, the i lly mounted at one endv to the underside of the main slide 56, is fulcrumed at the point 59 on the frame I of the machine and lever 51, pivota has a boss at its lower end contacting withthe surface of the cam BU. The cam 6U (Fig. 1) is mounted upon a vsleeve 6| which in turn is carried by the shaft 62. The cam shaft 62 is driven by means of the change gears B3, B4 and 65 from the drive shaft 9.A i'

The sleeve 6| carrying the cam 60 is removably mounted upon the end of the shaft 62 in the following rnanner':

The bearing 66 for 'the sleeve 6i is carried in a removable sleeve 61 mounted-inthe side wall of the frame l and held in such position ,by means of the socket head screwstuds B8. The

sleeve BI is connected to the shaft 62 through the anged coupling 69 and the hand wheel 1li, the latter making a splined or keyed t on the to the left hand endcf the hob H. Simultaneously, the cam `Gil is rotated at such a speed as to reciprocate the grinding wheel slide outwardly and inwardly with respect to the axis of the hob H as the rear end R of each tooth passes over-the grinding wheel and in the interval bef ore the next succeeding front end F is presented for grinding wheel contact. It will be noted that the teeth of the hob H are relieved from front to rear in a direction toward the center of the hob. This relief is alsosometimes termed back off or clearance In order to grind the hob teeth in accordance withlthis relieved contour, it'

- is necessary that the grinding wheel have 'a slight infeed movement radially inward of the hob as it traverses relatively with respect to the hob from the front to the rear end of the teeth. This radially inward feed movement of the grinding wheel is effected by means of the slow rise portion upon the cam 60.'

Thus, it will be seen that the grinding wheel. in grinding the `side A of a single tooth, is first fed radially inward towardihe axis of rthe hob at a relatively slow rate, and upon reaching a. point coincident with the rear end R of the tooth, or at the end of the grinding cut, is moved relatively rapidly outwardly from the axis of the hob.

After all of thessiges A of the hob have been ground from therighHdjto-the-left hand end of the heb H 'fin the case dfanghtmrhob having its helical rows of teeth disposed in a right hand helix), the hob H is turned end for end upon the spindle 2 and the latter is axially traversed to its farthest right hand position with respect to Fig. 1 whereby the grinding wheel G contacts with the opposite side face B of the hob .tecth. beginning at the left hand end of the hob in its reversed or turned position. The driving mechanism of the grinding machine is now reversed so that the hob H in its new position upon the-spindle v2 will again turn in a direction toward the front end F of its teeth. The grinding wheel G will'be seen to remain in its same relative position with respect to the hob axis, subject,

ofcourse', to minor adjustments for depth of cut, I hob tooth flank angle, etc.

.l Asfthe driving mechanism of the machine is reversed, the hob H turns in the direction as indicared by the arrow in Fig. 12, and the reciprocating action of the grinding wheel slide 56 remains Vthe same as in the previously described case of Fig. 10. viz., the grinding wheel moves slowly inwardly toward the axis of the hob H and rapidly outward. Since the cam shaft 62 'is also reversed in direction of rotation, it is necessary to reverse the cam 60 thereon so that the same sequence of reciprocating movements of the grinding wheel slide 56 will be retained.

Upon such reversal of the machine, the involute cam 34 also reverses its direction of rotation and Y. moves in a clockwise direction with respect to Fig. l whereby the hob H is axially traversed in a direction from right to left with respect to the grinding wheel G, and starting at the left hand end of the hob H, all of the sides B of the hob H are ground from end to end.

As a result of the above-described hob grinding process, it will be seen that the only manipulating which is required is that of turning the hob end for end upon the hob spindle, minor adjustment of the grinding wheel position for necessary cut and change of tooth ank angle, and reversal of the cam 60. The first and last of these manipulating steps are not* susceptible of variation or introducing any errors into the hob grinding operation, either through the action of the machine or through variations in human judgment or vision in changing from one operation to the other The minor re-adjustment of the grinding wheel as the hob is turned end for end is a manipulation dependent upon human judgment and skill; however, it is one which is required in any event in the lirst instance When the grinding wheel and the hob are set to the proper relative positions for instituting grinding operations. It will thus be seen that the opportunities for error incident to any human manipulations of the hob and of the grinding wheel are reduced to a minimum in the practice of the grinding process embodying the principle of my invention. Further, it will be noted that when the sides B of the hob teeth are ground that the axial traverse of the hob and hob spindle is controlled and determined by one and the same controlling surface, viz., the surface of the involute cam 34, and at the same timed movement relationship, as when the teeth sides A were ground. This eliminates any new set of machine-imparted errors from being introduced into the axial traverse of the hob as the change ismade from grinding one side of the teeth to the other side.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the means and the steps herein disclosed, provided those stated by any of the following claims or their equivalent be employed.

I therefore particularly point out and distinctly claim as my invention:

l. In' a grinding machine in which the workpiece is uniformly axially traversed and rotated on a xed axis, the combination of a rotatable and axially movable Work support, and an involute cam rotatable on an axis coinciding with the center of the base circle of its involute surface and normal to that of said work support for transmitting axial movement to the latter, the point of movement transmission from said cam being on a tangent to such base circle.

2.In a grinding machine in which the Workpiece is uniformly axially traversed and rotated on a fixed axis, the combination of a rotatable and axially movable work support, an involute cam rotatable on an axis normal to that of said work support for transmitting axial movement to the latter, said work support having a surface adapted to be contacted by said cam on a line tangent to the base circle of the involute, driving means for rotating said work support, and a gear train connecting said driving means to said cam for rotating the latter in timed relation to the rate of rotation of said work support whereby a given point radially removed from said work support moves in a helical path.

3. In a grinding machine in which the workpiece is uniformly axially traversed and rotated on a xed axis, the combination of a rotatable and axially movable work support, an involute cam rotatable on an axis normal to that of said work support for transmitting axial movement to the latter, said Work support having a surface adapted to be contacted by said cam on a line tangent to the base circle of the involute, driving means for rotating said Work support, and a reduction gear train so connecting said driving means to said cam as to rotate the latter a portion of a revolution during a multiple number of revolutions of said Work support, whereby a given point radially removed from the axis of said work support moves in a helical path.

4. .In a. grinding machine in which the workpiece is uniformly axially traversed and rotated on a fixed axis, the combination of an axially slidable and rotatable work spindle journaled on a fixed axis, and cam means mounted onan axis normal to, and laterally spaced from, that of said spindle, said cam means having an involute surface directly contacting one end of said spindle on a line tangent to the base circle of such involute surface g whereby rotation of said cam means about the center of such base circle produces longitudinal axial movement of said spindle.

5. In a grinding machine in which the work- .piece is uniformly axially traversed and rotated on produces longitudinal axial movement of said spindle, driving means for rotating said spindle, and a 4gear train. connecting said driving means to said cam means for rotating the latter in timed relationto the rate of rotationy to said spindle whereby agivenpoint on -said spindle moves in a helical path. f

6. In a. lgrinding machine in which the workpiece is uniformly axially traversed and rotated on a fixed axis,the combination ofan axially slidable and rotatable work spindle journaledon a fixed axis, cam means mounted on an axis norm-alto that of saidspindle, said cam means havingan involutesurf'ace directly vcontacting one end of said spindle on a line tangent to the base circle of such involutesurface whereby rotation of said camV` means'about: thecenter of such base` circle pro-` duces longitudinal axis movement of said spindle, driving means for rotating said spindle,` and a reduction gear ,train so connecting said driving means tosaid carnmeans as to rotate the latter a portion of a revolution during a of revolutions of said spindle whereby a point on the latter moves ina helical path. 1

7. In a grinding machine in which the workpiece is uniformly axially traversed `and'rotated on a fixed axis, the combination of an axially slidable and. rotatable work spindle journaled on a iixed axis, and an involutev Cam mounted onan axis coinciding with the center of the base circle of its involute surface and normalto that of 'sa-id spindle and having its camA surface Abearing against one end of said spindle on a line tangent to such base circle whereby produces longitudinal axial movement of said spindle.

8. In a grinding machine in which the workpiece is uniformly axially traversed and rotatedon a fixed axis, the combination of an axially slidable and rotatable work spindle journaled on a fixed rotation of said camy y multiple number 'I taining said spindle in contact with 'said cam during both directions of rotation` ofthe latter.

11. In a machine for grinding hobs and the like, the combination of an axially vslidablel and rotat able work spindle journalecl on a fixed axis, a grinding wheel carriage l--reciprocable in a direction transverse to the cam mounted on 'anaxis coincidiing with the center of the base .circle of its involute surface and normal to that of Vsaid spindle and bearing against one en d thereof on a line tangent to such base circle, driving means for rotating said'spindle for reciprocating said carriage and for `rotating said cam in timed relationship,'and gravity-.operated means connected to said spindle `for holding the latter against said 'cam'. f I

" 12; in a machine for grinding hobs and the like.

the combination of anaxially slidable and rotatable work spindle journaled onv a fixed -axis,`a. grinding wheel carriage reciprocablein a direction transverse to the axis of said spindle, an `involute cam mounted ron an'` axis coincidingwith the cen ter ofthe base` circle of its involute surfaceand normal to that of said spindle' and bearing against one end thereof-'onl a line tangent to `such' base circle,driving means for rotating said spindle, a

- reductiongear train sorconnecting said driving means tosaidl cam as to rotate the lattera portion of ya revolution duringy a multiple number of rev'-` olutions of said spindle, and a second gear train connecting said driving means to said'tool carj-y riage forv reciprocating thelatter at almultipl'e` number of reciprocations per revolutionoffsaid spindle.V

13. In a machine the combination of an axially slidable 'and rotat`` axis, an involute cam mounted on an axis coinciding with the center of the base circle of its involute surface and normal to that of said spindle and having its cam surface bearing against one end of said spindle on a circle whereby rotation of said cam produces longitudinal axial movement of said spindle, and

line tangent to such baselable workspindle journaled on a iixed axis,l a grinding wheel carriage reciprocable in a. direction transverse to the axis of said spindle, an involute cam mounted on an axis coinciding with the 'center of ,thel base circle of its involute 4surface and normal to that of said spindle and bearing against means for maintaining said spindle in Contact with said cam during both directions of rotation l of the latter.

9. In a machine for grinding hobs and the like, the combination of an axially slidable and rotatable work spindle journaled on a fixed axis, a grinding wheel carriage reciprocable in a direction transverse to the axis of said spindle, an involute cam mounted on an axis coinciding with the vcenter of the base circle of its involute surface and normal to that of said spindle and bearing against one end thereof on a line tangent to such base circle, and driving means for -rotating said spindle, for reciprocating said carriage and for rotating said cam in timed relationship.

l0. In a machine for grinding hobs and the like,A`

the combination of an axially slidable and rotatable work spindle journaled on a fixed axis, a grinding wheel carriage reciprocable in a direction transverse to the axis of said spindle,.an involute cam mounted on an axis coinciding with the center of the base circle of its involute surface and normal to that of said spindle and bearing against one end thereof on a line tangent to. such base circle. driving means for rotating said spindle, for

reciprocating said carriage and for rotating said cam in timed relationship, and means for mainone end thereof on aline tangent to such base circle, vdriving means for rotating said spindle, a worm wheel anda worm connected to said cam for vrotatingthe latter, a gear train connecting said driving means to said worm whereby said cam isrotated a portion of a revolution during a multiple number of revolutions of said spindle, and a second gear train connecting said driving means to said tool carriage for reciprocating the latter at a multiple number of reciprocations per revolution g lof said spindle.

14. In a machine for grinding hobs and the like,

the combination of an axially slidablefand ro` tatable work spindle journaled on. a fixed axis, ai

grinding wheel carriage reciprocable in a direc- .tion transverse to the axis of said spindle, an

involute cam mounted 'on an axis coinciding with the center of the base circle of its involute surface and normal to that of said spindle and bearing against one end thereof on a line tangent to such base circle, driving means for rotating said spindle, a worm wheel and a worm connected to said cam for rotating the latter, a gear train connecting said driving means to said worm whereby said cam is rotated a portion of a revolution during a multiple number of revolutions of said spindie, a second gear train connecting said driving means to said tool carriage for reciprocating the latter at a multiple numberof reciprocations per revolution of said spindle, and gravity operated means connected to said spindle for holding the latter against said cam.

15. The method of grinding hobs, consisting in `axis of said spindle,van involute for grinding hobs andthe like,

the steps oi rotating a hob about its axis, grinding one side of the teeth of said hob. beginning at one end thereof and ending at the other, turning said hob end for end, reversing the `direction of rotation of said hob, grinding the other side of said teeth, beginning at said other end of said hob and ending at said one end, and axially traversing said hob during each of the aforesaid grinding operations.

16. The method of grinding hobs, consisting in the-steps of rotating the hob about its axis in a direction toward the front end of its teeth, positioning a grinding wheel against one side of said teeth grinding said one side of said teeth, turning said hob end for end, rotating it in a direction toward the front end of its teeth while so turned, grinding the other side of said teeth, and axially traversing said hob during each of the aforesaid grinding operations.

17. The method of grinding-heirs, consisting in the steps of rotating a hob about its axis in a direction toward the front end of its teeth, positioning a grinding wheel against one side of said teeth grinding said one side of said teeth, Iwhile axially traversing said hob from one end to the other with respect to said grinding wheel, turning Said hob end for end and rotating it in a direction toward the front end of its teeth while so turned, and then axially traversing it in a direction opposite to that of the aforesaid direction of traverse with respect to said grinding wheel and simultaneously positioning the latter against the other side of said teeth.

18. The method of grinding hobs having relieved teeth, consisting in the steps of rotating a hob about its axis in 'the 'direction toward the front of its teeth, positioning a grinding wheel against one side of a tooth of said hob, moving said grinding wheel toward the axis of said hob at a. relatively low rate during rotation of the latter, moving said grinding wheel outwardly of such axis at a relatively rapid raie when it reaches a position coincident with the rear of 'said toothy turning said hob end for end and rotating it in a direction toward the front of its teeth while so turned. positioning said grinding wheel against the other side of said toothy and 'moving said grinding wheel axially outwardly and inwardly with respect to said hob in the same manner as aforesaid.

19. The method of grinding hobs having relieved teeth. consisting in the steps of mounting a hob on a rotatable spindle, reciprocating a grinding wheeLagainst one side of the hob teeth inwardly at a slow rate and outwardly at a rapid rate with respect to the hob axis during rotation ofthe latter, traversing said hob longitudinally with respect to said grinding wheel and therein;` grinding one side of all of the teeth of said hob. reversing the position of said hob on the spindle reversing the direction of rotation of the spindle, reciprocating `said grinding wheel in tht aforesaid manner against the other side of said hob teeth, and reversing the direction of longi tudinal traverse of said hob with respect to said grinding Wheel to grind the other side of all of the teeth of said hob.

LIONEL A. SCHMIDT. 

